Part of the DLNA system is that the Renderer (the bit that plays a file) lets the Server (MC) know what formats it supports. MC will then either transfer the file as is, or if needed do an on the fly transcoding. In either case, the file is then streamed to the DLNA Renderer and as long as the connection is faster that the playback rate you are all good. The only time I've seen issues is bandwidth constraints is on WiFi or Mobile networks. The key part would be the overall bitrate being sent vs the sustained bitrate of the connection. The size of the file in itself makes no difference.
Also - there can be issues if the transcoding part of the process is not fast enough to keep up. This will be a combination of the type of the Source File, the type of the Target File for transcoding and the compute power you have. For example, I can not stream out a 4K/60p UHD Blu-ray as MC is too slow to transcode in real time but all other files are fine for me. Note: At present some of the transcoding is single core and I know it is on Hendrik's (long) list to look at one day.... but in general you should be fine.